The present invention relates to the field of telephone systems and particularly to message metering systems for detecting and storing information concerning each subscriber's use of the telephone system.
Message metering equipment is necessary for recording information resulting from toll, long distance and other types of telephone service. Such equipment requires the ability to detect and store information to enable usage-sensitivity charging of subscribers. Local use by subscribers has been on a non-usage-sensitive basis employing equipment which has not been readily adapted for economical metering. With new types of local telephone usage such as credit-card checking, time-sharing data transmission and burglary prevention, a need for detecting and storing information concerning the nature of local usage has become important.
One message metering system suitable for local metering is described in U.S. Pat. No. 3,818,456. In that system, each local subscriber circuit is periodically addressed and connected to a digital encoder by a scanner bank. The digital encoder senses multistate subscriber signals representing usage and forms digital data. The digital data is transmitted to a scanner bank adapter where it is analyzed by the system and stored as usage data in internal memory locations for each individual subscriber. The internal memory storage locations are addressed in a sequential manner which corresponds to the sequential addressing of the subscriber circuits. Each time an internal memory location and a corresponding subscriber circuit is addressed, a multistate subscriber signal is sensed, interpreted and usage data is stored. The usage data is thereafter transferred from the internal memory to a larger-capacity external storage unit over data paths.
In the U.S. Pat. No. 3,818,456, the usage data output from each scanner bank adapter is connected using either one of two redundant data paths. The active states of redundant data paths are determined by an output and control unit. Specifically, the redundant data paths are interlocked by control networks of the type described in the cross-referenced application Ser. No. 365,045.
Because the system in the U.S. Pat. No. 3,818,456 is highly reliable, a need exists for extending the operation of that system to remote central offices, called tributary offices. Unattended tributary offices are frequently not suitable for collecting and processing data. It is often desirable to centralize the data collecting facilities so as to benefit from the economies of larger size.
In view of the above background, it is an objective of the present invention to provide a message metering system in which local recording offices and remote tributary offices are connected together in overall message metering systems of high reliability.